Bilinguals have powerful language control. They seem able to effortlessly switch between languages during conversation, but seldom produce words in an unintended language. A growing consensus in research on bilingualism is that executive control is the basis for language control, a hypothesis which led to the discovery of bilingual advantages in non-linguistic tasks involving executive control. Additionally, fMRI studies report similar brain regions active during task and language switching. Although this evidence is compelling, subtle differences between task and language control may be overlooked. We propose a powerful way to test the hypothesis that bilinguals rely on general executive control to achieve language control, by comparing language switching and task switching directly in the same group of individuals. Aim 1 of the proposed study will investigate age effects associated with task and language switching. Older adults appear to exhibit marked age-related shifts in executive function and language control. If task-switching and language-switching are analogous processes, performance on each of the two tasks will be related such that older adults who have preserved executive functioning abilities will have preserved language control abilities. Aim 2 of the proposed study adds a neuroimaging component that investigates language switching and task switching in the same group of individuals. Such a comparison allows for a well-controlled investigation of the regions involved in each task. Similar patterns of activation between task switching and language switching in bilinguals will suggest similar mechanisms underlying language control and executive control. Alternatively, dissociable patterns in language switching and task switching in bilinguals suggest additional mechanisms underlying language control not fully explained by executive control. In both experiments a group of matched monolingual controls will provide further leverage for identifying processing mechanisms unique to bilinguals. The proposed study will elaborate models of bilingual language control, executive control and its role in language processing, the aging language system, and will provide the applicant with skills necessary for leading a successful career in the field of bilingualism and aging. PUBLIC HEALTH RELEVANCE: Between1990 and 2000, the number of people who spoke a language other than English increased by 15 million. In addition, approximately 20 percent of people living in the United States are bilingual. Given the growth of bilinguals in the population, understanding mechanisms behind bilingualism is becoming increasingly important. Additionally, bilinguals offer a unique opportunity to investigate possible relationships between executive control and language processing. The proposed study intends to reveal cognitive and neural mechanisms supporting bilingual language control, and the consequences of aging and bilingualism for executive control. The results will also inform the development of valid cognitive assessments of bilinguals.